The latest module in our CPD series examines the regulations, standards, materials and other key factors to consider when designing pipework layouts. This module is sponsored by Marley Plumbing & Drainage

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How to take this module

UBM鈥檚 CPD distance-learning programme is open to anyone seeking to develop their knowledge and skills. Each module also offers members of professional institutions an opportunity to earn between 30 and 90 minutes of credits towards their annual CPD requirement.

This article is accredited by the CPD Certification Service. To earn CPD credits, read the article and then click the link below to complete your details and answer the questions. You will receive your results instantly, and if all the questions are correctly answered, you will be able to download your CPD certificate straight away.

CPD CREDITS: 60 MINUTES

DEADLINE: 28 AUGUST 2015

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This module is sponsored by Marley Plumbing & Drainage

INTRODUCTION

This CPD will outline the key considerations when designing pipework layouts for sanitary systems in accordance with the British and European standard BS EN 12056: 鈥淕ravity drainage systems inside buildings鈥. The precise size and design of a system will depend on factors such as building height and use and the number and type of appliances that discharge into it. However, all systems have key elements in common, including the use of water-sealed traps and a detailed ventilation strategy.

The Summit, a 22-storey student residential block in Leicester, uses PVCu soil and waste systems provided by Marley Plumbing&Drainage

The Summit, a 22-storey student residential block in Leicester, uses PVCu soil and waste systems provided by Marley Plumbing & Drainage

RELEVANT STANDARDS

A number of regulations and standards must be adhered to in the design of a sanitary pipework system, depending on location and scope of work. The current British standard has evolved from the London City Council drainage byelaws dating back to 1875. This was followed by a British standard on sanitary pipework, BS CP 304, in 1953 and 1968, and by BS 5572 in 1978 and 1994. In 2000, BS EN 12056 was introduced; part 2 of the standard relates to sanitary design.

Since 1965, the design of sanitary systems has been controlled nationally by Part H of the 好色先生TV Regulations: Drainage and waste disposal. Although this gives guidance on system design, it simply states that the system must be adequate. The designer can prove that it is by following a credible design strategy 鈥 for example, based on BS EN 12056:2 and the use of products certified by the British Standards Institute (BSI ) or the British Board of Agr茅ment (BBA).

TRAPS

Different countries use different design criteria for sanitary systems, but in the UK they are based on the use of water-sealed traps, which prevent foul air from entering the building. These should be installed at all points of discharge into the system and need to retain a minimum seal of 25mm of water or equivalent. The table below gives minimum trap sizes for common sanitary appliances.

Traps come in various configurations, such as low-level bath and shower traps for fitting in shallow spaces, anti-siphon bottle traps, which can be used under washbasins with a vertical pipe or long run of pipe, and 鈥淪鈥 or 鈥淧鈥 tubular traps. They should be attached immediately below the outlet, or as close as possible, and should be designed so that they are easily accessible.

ApplianceDiameter of trap (mm)Depth of seal (mm)
Washbasin, bidet3275
Bath, shower4050
Urinal bowl, sink4075
WC pan, outlet <80mm7550
WC pan, outlet >80mm10050

PIPEWORK MATERIALS AND JOINTS

A variety of materials are used for soil and waste pipework. They are covered by a number of different standards, as shown in the table below:

MaterialStandard
Soil pipework 
Unplasticised polyvinyl chloride (PVCu) 鈥 110mm 
and 160mm diameterBS EN 1329-1
PVCu 鈥 82mm diameterBS 4514*
High-density polyethylene (HDPE) 鈥 40-315mm diameterBS EN 1519-1
Modified polypropylene (PP-MD) 40-160mm 
diameterBS EN 1451 / 1411
Cast ironBS EN 877
Waste pipework 
Polypropylene (PP)BS EN 1451-1
Acrylonitrile butadiene styrene (ABS)BS EN 1455-1
Chlorinated polyvinyl chloride (PVCc)BS EN 1566-1

Each material is jointed in a different way:

  • PVCu soil pipes can either have a ring seal, which means they push-fit together, or they can be solvent welded
  • HDPE soil pipes are jointed by electrofusion or butt-welding, which is quick and simple but requires the use of specialist equipment. Push-fit joints are also required to accommodate thermal movement
  • ABS and PVCc waste pipes are solvent-weld jointed
  • PP acoustic soil and waste pipes can only be jointed using the push-fit method
  • Polypropylene waste pipes are push-fit jointed.

Branch pipes serving a single appliance should have at least the same diameter as the appliance trap.

Marley鈥檚 eight-way collar boss, which has four top and four side entries, was used at The Summit in Leicester

Marley鈥檚 eight-way collar boss, which has four top and four side entries, was used at The Summit in Leicester

DISCHARGE STACKS

Branch pipes connect to a central stack which discharges to a drain. When designing the stack, a number of factors need to be considered.

  • Positive pressure. To eliminate positive pressure, the minimum distance from the base of the stack to the lowest branch connection varies depending on the height of the stack, as the table shows:
ApplicationMinimum height
Single dwelling up to three storeys450mm
Up to five storeys740mm
More than five storeysOne storey
More than 20 storeysTwo storeys

The stack base should use two 45藲 bends or a bend with a radius of 200mm or more.

  • Stub stacks. Branch pipes can also discharge into an unventilated 鈥渟tub stack鈥 as long as they are only used to connect ground-floor appliances. The vertical drop to the drain must not exceed 1.5m from a WC and 2.5m from a waste appliance. The head of the drain should be vented to the atmosphere. The maximum loading of a stub stack is 5 litres/second.

Astor House, a 拢21m student residential building in Plymouth, uses Marley鈥檚 HDPE soil and waste products and eight-way collar boss

Astor House, a 拢21m student residential building in Plymouth, uses Marley鈥檚 HDPE soil and waste products and eight-way collar boss

  • Ventilation. Discharge stacks need to be ventilated in order to prevent the water seal in the trap from being broken by a pressure build up in the system. A secondary ventilation stack is sometimes required to increase stack capacity due to the number of appliances connected. The table below shows the different options depending on the calculated flow rate of the system.
Stack size (mm)Vent (mm)Maximum capacity (litres/second)
Primary ventilated stack  
82n/a2.6
110n/a5.2
160n/a12.4
Secondary ventilated stack  
82503.4
110507.3
1608218.3

Another option is to specify an aerator, which eliminates the need for secondary venting by breaking the flow on each floor, thereby keeping the pressure difference well within the limit of 3mbar. A 110mm aerator can increase the stack capacity to 7.3l/s.

Branch pipes will not need separate ventilation as long as they do not exceed the length and gradient shown in the following table:

ApplianceMaximum run (m)Gradient (%)Number of bendsMaximum drop (m)
Washbasin or bidet with 32mm-diameter pipe1.71.8-2.2None0
Washbasin or bidet with 40mm-diameter pipe31.8-4.420
Bath or shower31.8-9.0No limit1.5
Sink31.8-9.0No limit1.5
Washing machine or dishwasher31.8-4.4No limit1.5
WCNo limit1.8 minNo limit1.5
Sink disposer313.5 minNo limit1.5

If a branch pipe exceeds these limits, it should be connected via a branch ventilated pipe to external air or a ventilating stack, or an air admittance valve should be used.

An air admittance valve can be used to terminate primary vented discharge stacks, providing the air flow rate of the valve is at least eight times the peak flow rate on the stack.

Marley鈥檚 soil and waste design for the Hale Village housing scheme in north-east London reduced the number of soil stacks, requiring 35% less pipework

Marley鈥檚 soil and waste design for the Hale Village housing scheme in north-east London reduced the number of soil stacks, requiring 35% less pipework

  • Size of stack. In order to work out the correct size of the stack for a specific system, the designer has to add up the number of discharge units and for each one apply a factor depending on the type of use 鈥 for example, a house, school or hospital. The procedure and calculation method are explained in Tables 2 and 3 and clause 6.3 of BS EN 12056-2.
  • Prevention of cross-flow. A branch pipe should not discharge into the stack in a way that could cause cross-flow into any other pipe. To prevent cross-flow from a large-diameter branch into a smaller connection, the latter should join the stack in one of the following ways:
    • Above the centre line of the larger branch
    • At right angles to the larger branch
    • At least 200mm below a restricted zone beneath the centre line of the larger branch. The depth of this zone is determined by the diameter of the stack: 90mm for an 82mm stack; 110mm for a 110m stack; 250mm for a 160mm stack.
    Specially designed fittings can also alleviate this problem, such as the eight-way collar boss, which has four vertical and four horizontal connections. To link multiple WCs to a soil stack, a manifold system is used, varying the angle of the connector at each WC.
  • Offsets. Due to the design of commercial buildings, discharge stacks often need to be offset. When calculating the required flow capacity, the stack cannot be sized as a secondary ventilated system unless vent connections are incorporated on every floor. No connection is permitted within 450mm of the offset.

To book a CPD seminar at your office, email marketing@marleypd.com

CPD logo

How to take this module

UBM鈥檚 CPD distance-learning programme is open to anyone seeking to develop their knowledge and skills. Each module also offers members of professional institutions an opportunity to earn between 30 and 90 minutes of credits towards their annual CPD requirement.

This article is accredited by the CPD Certification Service. To earn CPD credits, read the article and then click the link below to complete your details and answer the questions. You will receive your results instantly, and if all the questions are correctly answered, you will be able to download your CPD certificate straight away.

CPD CREDITS: 60 MINUTES

DEADLINE: 28 AUGUST 2015

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